The fourth beta of OS X 10.11.6 has now been seeded to developers. We see this update one week after the last one. This is a minor update to OS X. Because of that, we only find some minor bug fixes and security improvements. There are no major changes that users will notice. That is because macOS Sierra is coming soon and brings lots of new features.
To get the latest build, developers can update in the Mac App Store. If you don’t have it yet, you can obtain the installer from the Apple Developer Center.